Xhosa Memetic Plague

This, in a weird way, could also potentially explain the greatly increased numbers of extremist opinions that are seemingly so widespread.

The following excerpt is from Where is My Flying Car:

The Xhosa are a southeast African tribe whose economy and culture were traditionally based on cattle-herding. In the spring of 1856, Nongqawuse, a 15-year-old girl, heard the voices of her ancestors telling her that the Xhosa had to kill all their cattle and destroy their hoes, pots, and stores of grain. Channeling the ancestors, Nongqawuse explained that once this had been done the very ground would burst forth with plenty, the dead would be resurrected, and the interloping Dutch-German Boers would be driven from their lands. Surprisingly enough, the beliefs found fertile ground among the Xhosa and spread like wildfire, within months receiving the imprimatur of their king.

Many members of the tribe slaughtered their cattle; by the end of 1857, over 400,000 had been killed. The Xhosa also refrained from planting for the 1856-1857 growing season, and as a consequence, there was no harvest. No cattle, no harvest. It is estimated that 40,000 Xhosans starved to death and that about an equal number fled the country in search of food. By the end of 1858, three-quarters of the Xhosa were gone.

It stands as a stark reminder that when social feedback, superstition, hopes and desires, and the suppression of doubt and skepticism in the name of faith line up, the resulting movement can make an entire people believe and do horribly self-destructive things that are completely at odds with common sense.